CD226 and neoplasm: Instead of two well-known immune checkpoint molecules PD-1 (programmed cell death protein 1, also named CD279) and PD-L1 (programmed cell death-ligand 1), other molecules such as CD155, CD226, and LAG3 are also recognized as new immune-related molecules which contribute to tumor-mediated immune suppression and promote tumor immunity escape in ESCC [7].